In Japan, a market of large-scale photovoltaic power generation systems such as a mega-solar power plant having an output of one megawatt or larger has been expanded by introduction of FIT (Feed-in Tariffs). Meanwhile, it is also considered that a market of maintenance such as detection and diagnosis of defects of the already-structured and operating photovoltaic power generation systems will be further expanded in the future.
Various techniques related to the detection and the diagnosis of the defects of the photovoltaic power generation systems, the photovoltaic cell modules, and others have been already suggested. For example, Japanese Patent Application Laid-Open Publication No, 2009-21341 (Patent Document 1) describes a technique of identifying a defective position in a photovoltaic cell array and a defective type by applying a measurement signal waveform to a part between a ground terminal and a terminal (positive electrode or negative electrode) of a photovoltaic cell string or a terminal (positive electrode or negative electrode) of a photovoltaic cell array and comparing the measurement signal waveform with a response signal waveform.
And, Japanese Patent Application Laid-Open Publication No. 2011-29541 (Patent Document 2) describes a technique in which a photovoltaic cell module has a plurality of photovoltaic cell panels and a movable member that is movable for shielding from at least a part of incident light that enters the plurality of photovoltaic cell panels, the technique diagnosing an operation state of each of the plurality of photovoltaic cell panels based on a moving state of the movable member.
And, International Publication WO/2015/022728 (Patent Document 3) describes a technique of measuring each of a first output current of a first photovoltaic cell string and a second output current of a second photovoltaic cell string, calculating a second temperature property of the second photovoltaic cell string based on a value of the first output current and a valine of the second output current, and determining whether the second photovoltaic cell string has a defective or not based on the second temperature property.